1. Field of the Invention
This invention relates to a stop valve used in a vacuum apparatus, and more particularly to a stop valve for a vacuum apparatus, which stop valve has a main valve portion of a large capacity and an auxiliary valve portion of a small capacity both provided in an air exhaust passageway.
2. Description of the Related Art
In a vacuum apparatus used in a manufacturing system of semiconductors and the like, it is necessary to increase the degree of vacuum in a chamber in a short time, and thus it is required that a stop valve provided in an exhaust passageway have a resistance as low as possible and a high capacity. At the initial stage of the drive of a vacuum pump, however, the use of such a stop valve makes the exhaust speed too fast, and a turbulent flow is likely to occur in the vacuum apparatus. This causes a problem that fine particles attached to the inner wall faces of a chamber or an exhaust pipe are apt to be scaled off and scattered.
As shown in FIG. 8, a typical vacuum apparatus which avoids this problem comprises a main valve a of a large capacity provided in an exhaust passageway c, an auxiliary valve b of a small capacity also provided in the exhaust passageway c and arranged in parallel with the main valve a in such a manner that only the auxiliary valve b is opened to make the exhaust speed low at the initial stage of air exhaust and the main valve is opened after the degree of vacuum has been enhanced to some extent.
However, this typical vacuum apparatus must be provided with two valves a and b arranged in parallel with each other. Thus, the apparatus is encountered with the problem that it is costly and requires a large space and the operation of the valves is cumbersome.